Optical channel plates with optical fibers or hollow waveguides

ABSTRACT

A method of forming a solid or honeycombed optical channel plate, having solid or hollow waveguides respectively, from aligned optical waveguides. Reflective optical channel plates are also disclosed for use with a front projection screen and transmission optical channel plates are also disclosed for use with a front projection screen and transmission optical channel plates for use with a rear projection screen for increasing luminance and/or resolution of an image projected on the screen.

This invention relates to reflection and transmission optical channelplates, in particular for use with display devices.

The use of optical channel plates, or face plates, in association withdisplay devices is known. For example, U.S. Pat. No. 5,911,024 disclosesa fibre optic display constructed from a plurality of short opticalfibres whereby an enlarged image can be produced from a cathode raytube. Similarly a front fibre optic face plate for use in a liquidcrystal display has been disclosed in, for example, U.S. Pat. No.5,959,711.

One application of the present invention is for front projectionscreens. The flat surface of known front projection screens is notshielded from stray light and reflections of the stray light from thescreen can degrade an image projected on the screen. Moreover, lightincident on the screen is scattered with only a small proportion of theincident light being reflected towards a viewer. In order to seek toovercome this problem, use has been made of metallised fabrics orplastics with some success but only for applications where the screen isviewed from a distance.

There are also problems with existing rear projection screens, such asthose used for large screen televisions, that when viewed at wide anglesthe image is subject to disturbing colour separation.

Problems also exist, which are common to front and rear projectionscreens, of diffusion of light from a single point on the screenresulting in a fuzzy image. This contributes to the fact that only verysmall viewing angles can be used for large screens, especially for rearprojection screens.

There are also particular problems with the use of cathode ray tubedisplays. In particular, the tubes have high power consumption andgeometric distortion is introduced by the displays. To overcome thegeometric distortion the displays require further magnetic elements inaddition to cathode ray tube deflecting coils. There is also a possibleproblem of harmful radiation levels from prolonged exposure to cathoderay tubes. Although liquid crystal displays potentially would overcomemany of these problems, liquid crystal displays suffer even more thancathode ray tubes from difficult viewing under strong lightingconditions, particularly due to reflections of stray or ambient lightfrom the screen.

It is an object of this invention to seek at least partially toameliorate these difficulties.

It is a particular object of the present invention to provide analternative method for the production of optical channel plates.

According to a first embodiment of a first aspect of the presentinvention there is provided a method for forming a solid optical channelplate comprising the steps of: a) providing optical fibres withrespective longitudinal axes in side-by-side relationship; b) usingmechanical aligning means to align the optical fibres in a twodimensional array with the respective longitudinal axes substantiallyparallel, to form a substantially regular geometric pattern incross-section; c) adhering the optical fibres together along at least aportion of their longitudinal surfaces; and d) transversely slicing thearray of optical fibres to form at least one optical channel plate.

Conveniently, the step of providing optical fibres in side-by-siderelationship includes heating and pulling the optical fibres to formtapering fibres.

Preferably, the step of providing optical fibres in side-by-siderelationship includes the step of coating the optical fibres withcoatings along longitudinal surfaces of the optical fibres to increaseinternal optical reflectivity of the optical fibres.

Advantageously, the step of coating the optical fibres includes coatingby electroplating.

Advantageously, the step of aligning the optical fibres with mechanicalmeans includes the step of aligning the optical fibres with ultrasonicvibrating means.

Conveniently, the step of adhering the optical fibres includesultrasonically vibrating the optical fibres such that portions of thecoatings of adjacent optical fibres are heated and welded together.

Alternatively, the step of the adhering the optical fibres comprisesusing adhesive.

Conveniently, the step of transversely slicing the array to form atleast one optical channel plate includes the further step, after slicingthe array, of polishing at least one of the opposed end surfaces of theoptical fibres, which together form opposed end surfaces of the at leastone optical channel plate.

Advantageously, the step of polishing the at least one of the opposedend surfaces of the at least one optical channel plate includes coatingone of the end surfaces of the at least one optical channel plate toincrease the internal optical reflectivity of the respective endsurfaces of the at least one optical channel plate, to form at least onereflective solid optical channel plate.

Conveniently, the step of providing optical fibres in side-by-siderelationship includes providing optical fibres having a circulartransverse cross-section.

Alternatively, the step of providing optical fibres in side-by-siderelationship includes providing optical fibres having a polygonal,preferably hexagonal, transverse cross-section.

According to a second embodiment of the first aspect of the presentinvention, there is provided a method of forming a honeycombed opticalchannel plate comprising the steps of; a) providing an array of alignedcoated fibres, the fibres having optically reflective coatings with amelting point higher than that of the fibres; b) transversely slicingthe array of coated fibres to form at least one plate of coated fibres;c) heating the at least one plate of coated fibres to melt the fibres toform molten fibre material; and d) removing the molten fibre materialfrom the at least one plate of coated fibres to leave the opticallyreflective coatings as hollow optical waveguides forming a honeycombedoptical channel plate.

Conveniently, the step a) of providing an array of aligned coated fibresincludes the steps of providing an array of aligned fibreslongitudinally spaced apart by longitudinal interstitial spaces; andpassing coating solution between the aligned, spaced apart, fibres tofill the interstitial spaces and thereby coat the fibres along theirlengths to form an array of coated fibres having optically reflectivecoatings with a melting point higher than that of the fibres, such thatthe optically reflective coatings cause the fibres to adhere togetheralong their lengths.

Advantageously, the step of providing an array of aligned, coated fibresincludes the step of aligning the fibres using ultrasonic vibratingmeans.

Conveniently, the step of providing an array includes heating andpulling the fibres to formed tapering fibres.

Advantageously, the fibres are coated by electroplating.

Conveniently, the step of providing an array of aligned fibres includesproviding fibres having a circular transverse cross-section.

Alternatively, the step of providing an array of aligned fibres includesproviding fibres having a polygonal, preferably hexagonal, transversecross-section.

Conveniently, the step of slicing the array to form at least one plateincludes coating a major face of the at least one plate with anoptically reflective end coating, such that the step of removing themolten fibre material from the at least one plate leaves the opticallyreflective coatings as hollow optical waveguides closed at one end bythe optically reflective end coating, to form a reflective honeycombedoptical channel plate.

According to a third embodiment of the first aspect of the presentinvention, there is provided a method for forming an optical channelplate comprising the steps of: a) providing an array of aligned opticalwaveguides interconnected in side-by-side relationship spaced apart byinterstitial spaces; b) clamping the optical waveguides in position withrespect to each other to form clamped optical waveguides; c)transversely slicing the array of waveguides to form at least oneclamped optical waveguide plate with interstitial spaces; d) filling theinterstitial spaces in the waveguide plate with optically reflectivecoating material to improve the internal optical reflectivity of thewaveguides and to adhere the waveguides together in the array; and e)unclamping the clamped optical waveguide plate to form an opticalchannel plate.

Conveniently, the step of providing an array of aligned opticalwaveguides includes using ultrasonic vibrating means to align theoptical waveguides.

According to a fourth embodiment of the first aspect of the invention,there is provided a method of forming an optical channel platecomprising substantially parallel hollow optical waveguides, the methodcomprising the steps of: a) providing a plurality of corrugated sheetsof optically reflective material; b) stacking the plurality ofcorrugated sheets one upon another to form substantially parallel spacedapart optical waveguides between adjacent stacked sheets; and c)adhering adjacent sheets to each other.

Conveniently, the step of providing a plurality of corrugated sheets ofoptically reflective material includes the step of coating sheets ofnon-optically reflective material with an optically reflective coating.

Conveniently, the step of providing a plurality of corrugated sheetsincludes the step of forming corrugated sheets from substantially planesheets by using pressing means to deform the substantially plane sheetsinto corrugated sheets while the sheets are in a ductile state.

Advantageously, the step of adhering adjacent sheets together includesthe further step of slicing the adhered sheets into separate channelplates.

According to a fifth embodiment of the first aspect of the presentinvention, there is provided a method of forming an optical channelplate comprising substantially parallel optical waveguides comprisingthe steps of: providing a block of material; and b) machining the blockto form substantially parallel optical waveguides therein.

Conveniently, the step of providing a block of material comprisesproviding a block of optically reflective material.

Advantageously, the step of machining the block includes the furtherstep of coating the substantially parallel optical waveguides withoptically reflective material to increase the internal opticalreflectivity of the optical waveguides.

Advantageously, the step of machining the block to form substantiallyparallel optical waveguides therein comprises forming solid opticalwaveguides of the material of the block.

Alternatively, the step of machining the block to form substantiallyparallel optical waveguides therein comprises forming hollow opticalwaveguides within the material of the block.

Conveniently, the step of machining the block to form substantiallyparallel optical waveguides therein comprises machining under numericalcontrol.

According to a second aspect of the present invention, there is provideda reflective optical channel plate for a front projection screen, theoptical channel plate comprising a plurality of optical waveguidesarranged in an array for location substantially perpendicular to a majorplane of the screen such that light of a projected image entering firstends of the optical waveguides is collimated by the optical waveguidesand reflected from opposed second ends of the optical waveguidesrespectively to be viewed after reflection with substantially nointerference from stray light reflected from the second ends of thewaveguides.

Conveniently, the optical waveguides are optical fibres.

Advantageously, the optical fibres are coated along their lengths toincrease internal reflectivity of the optical fibres.

Conveniently, the optical waveguides are adhered together along theirlengths.

Advantageously, the second ends of the optical fibres are coated toincrease internal reflectivity of the second ends.

Advantageously, the optical waveguides are hollow optical waveguides.

Conveniently, the array of hollow waveguides has a honeycomb structurein transverse cross-section.

Conveniently, the optical waveguides have a circular transversecross-section.

Alternatively, the optical waveguides have a polygonal, preferablyhexagonal, transverse cross-section.

Conveniently, the channel plate is arcuate in a plane substantiallyperpendicular to the axes of the optical waveguides such that thechannel plate forms a collimated convex or concave mirror.

According to a third aspect of the present invention, there is provideda transmission optical channel plate for a display screen, the opticalchannel plate comprising a plurality of optical waveguides forarrangement in an array substantially perpendicular to a major plane ofthe screen such that light of an image entering first ends of theoptical waveguides is collimated and transmitted from opposed ends ofthe optical waveguides respectively.

Conveniently, the optical waveguides taper from the screen to produce amagnified image on the screen and longitudinal axes of the waveguidesare at least partially arcuate such that light may enter ends of thewaveguides at an angle substantially within the plane the screen to forma substantially flat display device.

Advantageously, the optical waveguides trifurcate into three opticallyconnected sub-waveguides respectively such that light of differentcolours entering from each of the sub-waveguides respectively may becombined in each of the waveguides to illuminate a pixel on the screen,respectively.

Alternatively, the inner longitudinal surfaces of the waveguides arecoated with photoelectric material, for the emission of electrons.

Advantageously, the axes of the optical waveguides are arcuate toincrease the number of optical reflections from the coated innerlongitudinal surfaces.

Embodiments of the invention will now be described by way of exampleswith reference to the accompanying drawings, in which:

FIGS. 1 to 3 are cross-sectional views of portions of optical channelplates according to the present invention having optical waveguides ofhexagonal, circular and triangular cross-sections, respectively;

FIG. 4 is a perspective view of a portion of the optical channel plateof FIG. 1;

FIG. 5 is a perspective view of a portion of the optical channel plateof FIG. 2;

FIG. 6 is a perspective view of a means of aligning the optical fibresof the optical channel plate of FIG. 2, using ultrasonic vibrations,according to an embodiment of the present invention;

FIG. 7 is a partial cross-section of coated optical fibres of theoptical channel plate of FIG. 2;

FIG. 8A is a transverse cross-section of an array of optical fibres ofthe optical channel plate of FIG. 1;

FIG. 8B is a longitudinal cross-section of the array of FIG. 8A;

FIG. 8C—shows the array of FIG. 8A with a coating;

FIG. 8D—shows a longitudinal cross-section of the coated array of FIG.8C;

FIG. 8E—shows an optical channel plate formed from the array of FIG. 8D;

FIG. 9A—shows a transverse cross-section of fibres used in manufactureof a hollow optical waveguide channel plate of an embodiment of thepresent invention;

FIG. 9B—shows a longitudinal cross-section of the fibres of FIG. 9A;

FIG. 9C—shows the array of FIG. 9A covered with a coating;

FIG. 9D—shows a longitudinal cross-section of the coated array of FIG.9C;

FIG. 9E—shows a longitudinal cross-section of a slice formed from thecoated array of FIG. 9D;

FIG. 9F—shows a transverse cross-section of a hollow waveguide channelplate formed from the slice of FIG. 9E after melting and removing thefibre material;

FIG. 9G—shows a longitudinal cross-section of the hollow waveguidechannel plate of FIG. 9F;

FIG. 10—shows light rays reflected from the reflective optical fibrechannel plate of FIG. 8E;

FIG. 10A—shows light rays collimated and reflected from a transmissionoptical fibre channel plate of an embodiment of the invention;

FIG. 11—shows light rays reflected from the hollow optical waveguidereflective optical channel plate of FIG. 9G;

FIG. 11A—shows light rays collimated and reflected from a transmissionhollow optical waveguide channel plate of an embodiment of theinvention;

FIG. 12—shows a cross-section of a concave optical channel plate mirroraccording to the invention;

FIG. 13 & FIG. 14—show tapered optical fibres used in an embodiment ofthe present invention;

FIG. 15A—shows a flat display device using the tapered optical fibres ofFIGS. 13 & 14;

FIG. 15B—shows a cross-section of a line B—B of FIG. 15A;

FIG. 16—shows a trifurcated optical fibre for use in the presentinvention;

FIG. 17—shows an application of channel plates of the present inventionfor producing an image on a side of building, the image beingtransmitted from an opposed side of the building;

FIG. 18 is a perspective view of a machined block used in an embodimentof the invention for the production of an optical channel plate havinghollow waveguides;

FIG. 19 is a top view of the machined block of FIG. 18;

FIG. 20 is a perspective view of a further machined block used in anembodiment of the invention for the production of an optical channelplate having solid waveguides;

FIG. 21 is a perspective view of cylinders machined from the block ofFIG. 20;

FIG. 22 is a top view of the cylinders of FIG. 21;

FIG. 23 is a perspective view of the cylinders of FIGS. 21 and 22embedded in support material;

FIG. 24 is a top view of the cylinders of FIG. 23;

FIG. 25 is a schematic view of a sheet of material and opposed dies usedin an embodiment of the invention;

FIG. 26 is a schematic view of the sheet and dies of FIG. 25, showingthe dies deforming the sheet to form a corrugated sheet;

FIG. 27 is a schematic view of a corrugated sheet of FIG. 26; and

FIG. 28 is a schematic view of a stack of corrugated sheets of FIG. 27.

In the Figures like reference numerals denote like parts.

As shown in FIGS. 1 to 5, the optical channel plate of the presentinvention employs an array of aligned optical waveguides 10,11 or 12which in the case of hexagonal 11 or triangular 12 cross-sections, asbest shown in transverse cross-section of FIGS. 1 and 3, are closelypacked with small interstitial spaces 115, 125 but are packed with largeinterstitial spaces 105 where the cross-section 10 of the waveguide iscircular as shown in FIG. 2.

In one embodiment of the invention the waveguides are optical fibres. Inorder mutually to align the optical fibres 60 they may be assembled withtheir longitudinal axes horizontal and the optical fibres vibratedultrasonically in the plane of their longitudinal axes in two mutuallyperpendicular directions, as indicated by double arrow headed lines61,62 in FIG. 6, until the optical fibres fall into alignment undergravity. Alternatively, the optical fibres may be aligned by othermechanical means, for example, by centrifuging or under the influence ofgravity, preferably assisted by vibration of the fibres.

Referring to FIG. 7, before being aligned, the optical fibres 70 mayhave an external coating 71 applied to their longitudinal surfaces toimprove the internal optical reflectivity of the fibres. Alternatively,it will be apparent to those skilled in the art that graded index fibrescould be used wherein the index of refraction of the material of thefibre changes along the radius of the fibre, to improve the internalreflectivity.

The aligned optical fibres may then be adhered together by passingadhesive into and through the interstitial spaces 105,115,125 betweenthe fibres. This is particularly appropriate in the case of, forexample, fibres 10 with circular cross-section shown in FIG. 2.Alternatively, using coated fibres 72, the fibres may be adheredtogether at touching portions of adjacent fibres by ultrasonicallyvibrating the fibres causing local melting of the coating at points ofcontact and, hence, welding together the fibres, or by heating thefibres by other means. Alternatively a heat-activated, or other,adhesive may be used.

Referring to FIG. 8, in a third method of manufacture according to theinvention using an array of uncoated fibres 80, a coating solution maybe passed through the interstitial spaces 84 to both form a coating 81on the fibres and to bind the fibres 80 together in a bundle, see FIGS.8C & 8D. In the interests of clarity of the figures the fibres are shownrelatively further apart than they would be in practice. Such a coatingprocess may use known electroplating techniques. It will be apparentthat the third method of manufacture could also be used with precoatedfibres and additional coating material could be used to bind the fibrestogether.

In the case of closely packed bundles, some difficulty may beexperienced in passing either adhesives or coating solutions into theinterstitial spaces. The fibres may therefore, in such a case, beclamped together in a spaced apart configuration, as shown in FIGS. 8A &8B, rather than in their close packed configuration, shown in FIGS. 1 &3, to permit sufficient interstitial space for the passage of suchadhesive or coating solution. Alternatively, the fibres may be coatedafter they have been sliced into short lengths in a manner to bedescribed.

Once the array of optical fibres have been adhered together and/orcoated in a bundle, the bundle is sliced into channel plates 82 bycutting at an angle perpendicular to the axes of the fibres in a mannerknown per se. The end faces of the optical fibre optics are polished.Where a reflective optical channel plate is required one of the endfaces of the plate is then coated with a coating 83 of reflectivematerial.

Referring to FIGS. 9A-9G, in an alternative embodiment of the invention,hollow optical waveguides 90 are used rather than optical fibres 80. Inthis embodiment an array of fibres 93, not necessarily optical fibres,are formed as in the first embodiment. As in the first embodiment, thesefibres may be pre-coated or may be coated once assembled into the arraywith a coating 92 as described in the first embodiment. However, fibrematerial 93 is chosen which has a lower melting point than the meltingpoint of the coating 92 and subsequent to assembling the coated fibresand slicing the assembly into slices 95, the plates are heatedsufficiently to melt the fibre to form molten fibre material but toleave the coatings 92 unmelted. The molten fibre material is thenremoved from the slice to leave a honeycomb structure of hollowwaveguides 90 formed by the coatings 92. It will be appreciated that theremoval of the molten fibre material may be assisted by blowing throughthe honeycomb structure, where both ends of the channels are open.Alternatively, the removal of molten fibre can be facilitated bysuction.

In the case of the production of reflective optical fibre channels, oneof the faces of the slice 95 is coated with a end coating 96 before thefibres are melted so that a honeycomb structure is formed with one endclosed by optically reflective material.

A further embodiment of the invention is shown in FIGS. 18-24, in whichan optical channel plate is machined from a block of material 180, 200.In a first version of the embodiment as shown in FIGS. 18 and 19, anarray of cylindrical bores 181 are drilled in the block 180 to formoptical waveguides through the block. A perspective view of the drilledblock is shown in FIG. 18 and a top view of the drilled block is shownin FIG. 19. In the interests of clarity the cylinders and distances areshown magnified in the figures, and only an exemplary number ofcylinders are shown. In practice the cylinders may be drilled at afrequency of up to 10,000 holes/inch (4,000 holes/cm) using, forexample, numerically controlled machining. The internal surfaces of thecylindrical bores may be coated with an optically reflective coatingafter drilling, so that the block of material 180 need not necessarilybe of optically reflective material.

Although the cylindrical bores are shown as right circular cylinders, itwill be understood that any other cross-sectional shape, for examplecylinders having a hexagonal cross-section, may be machined instead.

As in embodiments previously described, the block may be slicedtransversely to the axis of the cylinders, to provide a plurality ofoptical channel plates with hollow waveguides.

A second version of this embodiment is shown in FIGS. 20 to 24, in whichmaterial of the block 200 is machined away to leave an array of solidcylinders 201 of the block material, as shown in perspective view inFIG. 21 and as an end view in FIG. 22. In this version of the embodimentthe block 200 is therefore necessarily of optically transparentmaterial. The cylinders may be coated to increase the internal opticalreflectivity of walls of the waveguides thus formed. As shown in FIGS.23 and 24 this coating, or other additional material, may be introducedin the interstitial spaces between the cylinders to act as a mechanicalsupport for the cylinders. As in the previously described version ofthis embodiment, the block 230 of cylinders embedded in support materialmay then be sliced if required to form a plurality of optical channelplates with solid waveguides, or the block may be used as a singleoptical channel plate. It will be understood that once again thewaveguides do not necessarily have a cylindrical cross-section but may,for example, have a hexagonal cross-section.

A further embodiment of the invention is shown in FIGS. 25 to 28. Inthis embodiment a sheet of material 250 is passed in direction ofarrow-headed line 251 between a first die 252 and an opposed offsetsecond die 253. The first die and the second die 253 each have a workinghead in the shape of a half hexagon. The sheet 250 may be paused with asection of the sheet 251 between the dies, and the first die 252 movedin the direction of the arrow-headed line towards the sheet to deformthe sheet and the second die 253 moved in an opposed direction to thatof the first die towards the sheet to deform the sheet, in the directionof arrow headed line 255, but offset from the first die. In this manner,first and second opposed corrugations 261 and 262 of half-hexagonalshape are formed in the sheet 250. The dies are then withdrawn and thesheet stepped forward in the direction of arrow headed line 251 to forma second pair of corrugations adjacent to the first pair to form acorrugated sheet as shown in FIG. 27. Some thinning of the sheet willnecessarily occur during pressing and this is allowed for in theoriginal selection of the thickness of the supplied sheet.

Although the dies have been shown and described as having working headswhich are in the shape of half hexagons, it will be understood thatdifferently shaped working heads may be used to form corrugations ofdifferent shapes, for example, semicircular working heads may be used.

It will be apparent that the sheet 250 must be sufficiently ductile tobe deformed into corrugations. In the case of a glass sheet thisductility may be achieved by working the sheet at a temperature aboveroom temperature at which the glass is ductile. Conveniently, this maybe done immediately after manufacture of the glass sheet before thesheet has cooled from the manufacturing process.

As an alternative to the discontinuous process described, in which thefirst and second dies 254, 255 move in a direction transverse to theplane of the sheet 250, a series of die heads may alternatively each bemounted on respective first and second offset drums (not shown) havingrespective axles parallel to the plane of the sheet so that the sheet iscontinuously passed between the respective drums such that successivedie heads on each respective drum deform the sheet. It will be apparentthat some adaptation of the shape of the die heads may be required toachieve the required corrugations in this case to allow continuousmovement of the sheet between the respective drums.

A number of corrugated sheets formed in this manner may then be stackedone upon another as shown in FIG. 28 to define channels therebetweenhaving, in the case of half-hexagonal dies, a hexagonal cross-section.As shown in FIG. 28, a plurality of such sheets may be stacked one uponanother to form an array of channels, in which the channels insuccessive layers are offset from each other. The corrugated sheets maybe transported and/or stacked using numerically controlled machinery.

Where the sheet 250 is of optically reflective material, these channelsform hollow waveguides. Where the sheets are not of optically reflectivematerial, or to increase the optical reflectivity, the inner surfaces ofthe channels may be coated with optically reflective material to formhollow waveguides.

The stacked corrugated sheets may be adhered together at the points ofcontact by any known method, dependent on the material of the sheets 25,for example they may be welded together or adhesive may be used. Wherethe sheets are of glass at an elevated temperature the sheets may bepressed together as the glass cools so that the sheets are meldedtogether.

It will be appreciated that the blocks of waveguides so formed may betransversely sliced if so desired to form a plurality of optical channelplates with hollow optical waveguides.

In one example of the embodiment the sheet of material is a metre widein the direction transverse to the direction of motion shown by arrowheaded line 251.

It will be appreciated that with suitable adaptation of the placementand shape of the dies, an optical channel plate with solid waveguidesmay be formed.

Referring to FIG. 10, for use as a front projection screen 100, or afront projection display, an image is projected from a projector ontothe uncoated or open ends of a reflective optical channel plate and thelight 101 from the projector is collimated by reflections 102 from theside walls 103 of the optical waveguides 104, non-specularly reflected105 from the end of the waveguides opposed to the end at which the lightenters the waveguides and further collimated by further reflection 106from the side walls 103 before emerging from the uncoated end of theoptical channel plate. A small portion 107 of the incident light 101 maybe reflected from the uncoated end of the optical channel plate.However, in general, stray light 108 entering the waveguides at an anglegreater than that at which the image enters will not be reflected backto a viewer to degrade the image. Some stray light 109 may be reflectedfrom the uncoated end face of the optical channel pate. In addition, thereflected light is collimated, so that a much larger proportion isreflected towards a viewer than would be in the case of light scatteredfrom a known screen without an optical channel plate. It will be evidentthat the invention, therefore, also has application wherever a highreflectively with collimation is required, for example, on vehiclereflectors or road signs. As shown in FIG. 11, the use of the hollowwaveguides 111 overcomes the problem of reflection from the front faceof the channel plate which may be experienced with a reflective opticalchannel using optical fibres. In this case incident stray light 118 islargely absorbed by repeated reflections within the hollow waveguide.

The reflective optical channel plate also has application in, forexample, large screen displays for reflecting images projected onto theside of a building.

Referring to FIG. 12, a further application of the reflective opticalchannel plate is for the production of concave 120 or convex mirrors byforming a reflective channel plate into a required concave or convexshape. Such optical channel mirrors, using specular reflections, haveparticular application in reflective telescopes for providing highreflectivity and reducing reflection of stray light.

It will be apparent that transmission optical channel plates located ona viewing side, or front, of a rear projection or phosphor screen cansimilarly be used to reduce the effect of reflection of stray or ambientlight from the front of the screen, to enhance the contrast of an imageprojected or produced on the rear of the screen, similarly to the use ofreflective optical channel plates illustrated in FIGS. 10 and 11.

In the case of transmission optical fibre channel plates, as shown inFIG. 10A, a rear projection beam 101′ incident on a rear projection orphosphor screen 1000 causes the scattering or emission of light,respectively, from the screen so that light rays 1001 are collimated byreflections 102′ from the side walls 103′ of the optical waveguides 104′before emerging from an uncoated end of the optical channel plate.However, in general, stray light 108′ incident on a viewing side of thescreen is weakly reflected 109′ from the surface of the waveguide butpredominantly is refracted 1009 into the waveguide and absorbed byrepeated reflections so that stray light does not interfere with theimage.

As shown in FIG. 11A, a hollow optical waveguide channel transmissionplate may be used without a scattering or phosphor screen. A rearprojection beam 111′, such as a laser beam, is scattered by reflections112′. Incident stray light 118′ on a viewing side of the screen is,however, absorbed by repeated reflections within the hollow waveguide,so as not to interfere with a viewed image produced by the light rays1101.

Transmission optical channel plates have particular application inassociation with flat displays. For example, by the use of taperedfibres 130, as shown in FIGS. 13 & 14, transmission optical channelplates can be used to produce an enlarged image by projecting an imageonto the small diameter ends of the tapered fibres to be emitted fromthe larger diameter end of the fibres. Such tapered fibres are known perse for use with displays from, for example, WO 97/38329 and FR 2628875in which the optical fibres are fabricated by drawing under gravity.

In a further application of the invention, waveguides may be used todeliver an image to the rear of a display screen, as shown in aschematic representation in FIGS. 15A & 15B, which show onlyrepresentative examples of the optical fibres of the channel platearray. Such a transmission optical channel plate using taperedwaveguides, can be used to produced extremely high resolution displays.For example, mechanical or quartz light rotators may be used to deliverhorizontal or vertical scans to the input ends 151 of the opticalwaveguides 152. As shown in FIG. 15B, the optical waveguides can becurved so that the entry points of the fibres are more or less in aplane of the display screen 153 which they are illuminating. In thisway, substantially flat display devices may be produced.

Bending of the optical waveguides of a transmission optical channelplate can also be employed to produce lenses, for example, for theconcentration of solar radiation in a manner analogous to the productionof a concave mirror shown in FIG. 12. A further application may be inspectacle lenses.

In a similar manner, where the waveguides are of photoemissive materialor are coated with photoemissive material, such channel plates may beused in photomultipliers. In one embodiment, the waveguides, ifelectrically conductive, are electrically insulated from each other, forexample, by an insulating coating. If photons are incident on the wallsof a waveguide, electrons will be emitted from the walls. If the channelplate is subjected to an electric field the electrons may subsequentlybe accelerated towards and be incident on a phosphor screen to cause theemission of light.

As shown in FIG. 16, colour mixing of displays can also be improved overknown displays by passing coloured light from three separate lightsources through single fibres 160 of an optical channel plate to beproduced in a required colour 161 at an emission end 162 of the fibres.This, for example, may be done by optically coupling three fibrestogether into the input of the waveguide of a transmission opticalchannel plate, the three fibres being illuminated by three differentlycoloured light sources 163,164,165. This overcomes the problem of colourseparation frequently encountered with large screen back projectiondisplays due to the physical separation, for example, of phosphors on ascreen for each of the three constituent colours. Because in this way acoloured pixel is produced with a single pixel rather than with threedifferently coloured pixels as in the prior art, a 3:1 increase inresolution of the screen is obtained.

Referring to FIG. 17, a further, large scale, application of thetransmission channel plates of the invention is the production of plateswhich bend around, or pass through a building 170 so that an input endof the plate covers, for example, one face 172 of the building and theoutput end of the plate covers an opposed face 173 of the building. Inthe interests of clarity of the figure, only representative examples ofthe optical waveguides of the channel plate array are shown in thefigure. In this manner, light received on one side of the building istransmitted to the opposed side of the building so that, if the inputand output of all the fibres are respectively aligned on either side ofthe building, an image of the view 174 as seen from one side of thebuilding is transmitted and displayed as an image 175 on the opposedside of the building, so that the building effectively becomesinvisible.

1. A reflective optical channel plate for a front projection screen, theoptical channel plate comprising a plurality of hollow opticalwaveguides arranged in an array for location substantially perpendicularto a major plane of the screen such that light of a projected imageentering first ends of the optical waveguides is collimated by theoptical waveguides and reflected from opposed second ends of the opticalwaveguides respectively to be viewed after reflection with substantiallyno interference from stray light reflected from the second ends of thewaveguides.
 2. A reflective optical channel plate as claimed in claim 1,wherein the hollow optical waveguides are hollow optical fibres.
 3. Areflective optical channel plate as claimed in claim 2, wherein theoptical fibres are coated along their lengths to increase internalreflectivity of the optical fibres.
 4. A reflective optical channelplate as claimed in claim 1, wherein the optical waveguides are adheredtogether along their lengths.
 5. A reflective optical channel plate asclaimed in claim 2, wherein the second ends of the optical fibres arecoated to increase internal reflectivity of the second ends.
 6. Areflective optical channel plate as claimed in claim 1, wherein thearray of hollow waveguides has a honeycomb structure in transversecross-section.
 7. A reflective optical channel plate as claimed in claim1, wherein the optical waveguides have a circular transversecross-section.
 8. A reflective optical channel plate as claimed in claim1, wherein the optical waveguides have a polygonal, preferablyhexagonal, transverse cross-section.
 9. A reflective channel plate asclaimed in any of claim 1, for a reflective telescope, wherein thechannel plate is arcuate in a plane substantially perpendicular to theaxes of the optical waveguides such that the channel plate forms acollimated convex or concave mirror.
 10. A transmission optical channelplate for a display screen, the optical channel plate comprising aplurality of optical waveguides for arrangement in an arraysubstantially perpendicular to a major plane of the screen such thatlight of an image entering first ends of the optical waveguides iscollimated and transmitted from opposed ends of the optical waveguidesrespectively wherein the optical waveguides trifurcate into threeoptically connected sub-waveguides respectively such that light ofdifferent colours entering from each of the sub-waveguides respectivelymay be combined in each of the waveguides to illuminate a pixel on thescreen, respectively.
 11. A transmission optical channel plate asclaimed in claim 10, wherein the optical waveguides taper from thescreen to produce a magnified image on the screen and longitudinal axesof the waveguides are at least partially arcuate such that light mayenter ends of the waveguides at an angle substantially within the planethe screen to form a substantially flat display device.
 12. Atransmission optical channel plate for a display screen, the opticalchannel plate comprising a plurality of optical waveguides forarrangement in an array substantially perpendicular to a major plane ofthe screen such that light of an image entering first ends of theoptical waveguides is collimated and transmitted from opposed ends ofthe optical waveguides respectively, for a photomultiplier wherein theinner longitudinal surfaces of the waveguides are coated withphotoelectric material, for the emission of electrons.
 13. Atransmission optical channel plated as claimed in claim 12, wherein theaxes of the optical waveguides are arcuate to increase the number ofoptical reflections from the coated inner longitudinal surfaces.